1. Field of the Invention
The invention generally relates to acoustic system testing devices and particularly to a towed array testing apparatus.
2. Description of the Prior Art
Flow noise in towed arrays results from convective energy due to turbulent wall pressure fluctuations on the surface of the array, and flow-induced vibrations of the array. Standard towed array designs are aimed at filtering convective energy using a combination of hydrophone size, hydrophone grouping as well as the stand-off distance between the hydrophone and the hosewall of the array.
Recent measurements made using experimental towed arrays, described by Keith and Cipolla (“Spectral Features of Wall Pressure Fluctuations Measured with an Experimental Towed Array,” NUWC TR 11,805, 26 March, 2007); Cipolla and Keith (“Measurements of the Wall Pressure Spectra on a Full Scale Experimental Towed Array,” Ocean Engineering, Vol. 35, Issue 10, July 2008, pp. 1052-1059); and Keith et al. (“Drag and Wall Pressure Measurements on a Towed Array Model at High Reynolds Numbers,” NUWC TR 11,855, Feb. 11, 2008) have shown the existence of low frequency spectral energy which extends across all measured wavenumbers.
Presently, the physics of this energy is not well understood. Comparison of the results presented by Cipolla and Keith and Keith et al. indicate that internal tension in the towed array may have a significant effect on these low frequency spectral levels. The complexity of the turbulent boundary layer wall pressure fluctuations and related fluid/structure interactions extremely limits purely analytical or computational approaches.
Full scale experimental efforts are very costly and time consuming. Laboratory testing which can provide results directly relevant to full scale arrays, and allow design parameters to be varied, are therefore very valuable.
Also known in the prior art is Keith et al., U.S. Pat. No. 7,130,242 B1, which is said to disclose a system and method for detecting an acoustic signal in the presence of flow noise produced by the turbulent flow field that develops about a hosewall of a towed array. Pressure is sensed with pressure sensors at two diametrically-opposed locations at the surface of the hosewall over a period of time. The sensed pressure signals are used to generate an ensemble-averaged cross-spectra which effectively cancels out the flow noise while retaining the acoustic signal associated with a possible target of interest.
Also known in the prior art is Keith et al., United States Patent Application Publication No. 20090303837, which is said to disclose a towed array having hot-film sensors and anemometer circuitry to calculate the angle of inclination of the towed array in real time during deployment of the towed array in a sea water environment. The hot-film sensors are arranged in pairs along the length of the towed array to increase the sensitivity of the inclination angle determinations and are located flush with an exterior surface of the towed array. The pairs of hot-film sensors determine the local sheer stresses on the towed array, and these measurements are converted to inclination angles using an empirically derived look-up table.
Based on existing knowledge of the prior art, there exists a need for convenient, inexpensive and rapid systems and methods for examining designs of towed arrays so as to provide towed array configurations that exhibit improved operational properties.